Two approaches that increase the activity of analogs of adenine nucleosides in animal cells

Deamination of many analogs of adenine nucleosides results in the loss of their chemotherapeutic efficacy. Two approaches have been used in this study to overcome this problem. First, some adenine nucleotides, which are resistant to mammalian adenosine deaminase, are more toxic to animal cells than are the respective nucleosides. For toxic to animal cells than are the respective nucleosides. For example, 9-beta-D-arabinofuranosyladenine 5'-phosphate, a molecule that penetrates the cell without degradation, has a more sustained toxicity against mouse fibroblasts (L-cells) than does 9-beta-D-arabinofuranosyladenine (ara-A). Furthermore, L-cells treated with 2',3'-dideoxyadenosine 5'-phosphate are extensively killed after 48 hr, whereas 2',3'-dideoxyadenosine is almost nontoxic to L-cells. Specific inhibition of adenosine deaminase by nontoxic concentrations of erythro-9-(2-hydroxy-3-nonyl)adenine greatly potentiates the biological activity of both ara-A and 3'-deoxyadenosine (cordycepin). Simultaneous administration of cytostatic concentrations of ara-A and the inhibitor of adenosine deaminase to L-cells killed greater than 99.9 percent of cells in 36 hr. A similar concentration of ara-A plus the deaminase inhibitor also markedly extended the mean survival of mice bearing Ehrlich ascites carcinoma as compared to ara-A alone. A cytostatic concentration of cordycepin 1 x 10-4 M), administered in the presence of deaminase inhibitor, killed greater than 99.9 percent of cultured L-cells in only 8 hr. During the latter incubation, accumulation of uridine in acid-insoluble material reached a maximum after 30 min, and incorporation of thymidine into acid-insoluble material was almost totally arrested after 2 hr.

Penetration of mouse fibroblasts by the 5'-phosphate of 9-beta-D-arabinofuranosyladenine and incorporation of the nucleotide into DNA

9-beta-D-Arabinofuranosyladenine 5'-monophosphate (araAMP) is more lethal to mouse fibroblasts (L cells) than the identical exogenous concentration of 9-beta-D-arabinofuranosyladenine (araA) (Cancer Res. 32, 1512, 1972). [(3)H,(32)P]AraAMP (0.1 mM) was taken into L cells for 4 hr in the presence of a large excess of (32)P(i). The radioactivity was subsequently found mainly in the adenine nucleotides in the acid-soluble fraction and in the cell DNA. The cellular concentration of 9-beta-D-arabinofuranosyladenine 5'-triphosphate (araATP) exceeded 2 muM. More than 90% of the (3)H was associated with araA in the nucleotides. After degradation of the adenine-containing triphosphates with apyrase, the adenine mononucleotides were separated by thin-layer electrophoresis and chromatography. All of the (32)P and 97% of the (3)H were associated with araAMP. The small amounts of (3)H and (32)P in the acid-insoluble material were similar during a 4 hr incubation. The DNA fraction was degraded enzymatically to 5'-mononucleotides. Both (32)P and (3)H were associated predominantly with 5'-dAMP. Most of the (3)H was in araA, detected after dephosphorylation. Enzymatic degradation of the DNA fraction to 3'-mononucleotides and fractionation revealed (3)H primarily in the 3'-adenine nucleotide and (32)P in each of the deoxynucleoside 3'-monophosphates. After dephosphorylation of the 3'-mononucleotides, 93% of the (3)H was found in araA. These results suggest that small amounts of araAMP penetrated the cell as an intact nucleotide, were further phosphorylated to the triphosphate, and subsequently incorporated in internucleotide linkage into DNA.